Cardiac arrhythmia, also known as dysrhythmia, refers generally to any of a group of conditions in which the electrical activity of the heart is irregular or is faster or slower than normal. Arrhythmias can occur in the upper chambers of the heart, or in the lower chambers of the heart. Arrhythmias may occur at any age. Some are barely perceptible, whereas others can be more dramatic and can even lead to sudden cardiac death.